Transmission apparatus, reception apparatus, and communication system

ABSTRACT

A transmission apparatus that transmits a block signal including a plurality of data symbols, includes: a data-symbol generation unit that generates a data symbol; a symbol arrangement unit that arranges the data symbol and a same-quadrant symbol such that one same-quadrant symbol that becomes a signal point in a same quadrant in a complex plane is inserted per block at a predetermined position in each block signal to generate a block symbol; a CP insertion unit that inserts a Cyclic Prefix into the block symbol; and an interpolation unit that performs interpolation processing on the block symbol on which CP insertion has been performed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 14/773,975filed Sep. 9, 2015, the entire contents of which is incorporated hereinby reference. U.S. application Ser. No. 14/773,975 is a 371 ofInternational Application No. PCT/JP14/056211 filed Mar. 10, 2014 andclaims the benefit of priority from prior Japanese Application No.2013-050930 filed Mar. 13, 2013.

FIELD

The present invention relates to a transmission apparatus, a receptionapparatus, and a communication system.

BACKGROUND

In a digital communication system, frequency selectivity and timevariability in a transmission line arise because of multipath phasingcaused by a transmission signal being reflected by buildings or the likeor Doppler variation caused by the terminal moving. In such a multipathenvironment, a received signal becomes a signal in which a transmissionsymbol and a symbol arriving after a delay time interfere with eachother.

With this kind of transmission line having frequency selectivity, asingle carrier block transmission method has recently attractedattention in order to acquire the best receiving characteristics (see,for example, Non Patent Literature 1 listed below). The single carrier(SC) block transmission system can reduce the peak power compared withan OFDM (Orthogonal Frequency Division Multiplexing) transmissionmethod, which is multi-carrier (Multiple Carrier: MC) block transmission(see, for example, Non Patent Literature 2 listed below).

With a transmitter that performs SC block transmission, measures againstmultipath phasing are taken by performing, for example, the followingkinds of transmission. First, after generating a PSK (Phase ShiftKeying) signal or a QAM (Quadrature Amplitude Modulation) signal, whichare digital modulation signals, in a “Modulator”, the digital modulationsignal is converted to a time domain signal by a precoder and an IDFT(Inverse Discrete Fourier Transform) processing unit. Thereafter, as ameasure against multipath phasing, a CP (Cyclic Prefix) is inserted by aCP insertion unit. The CP insertion unit copies a predetermined numberof samples behind the time domain signal and adds the samples to thehead of a transmission signal. In addition to this method, as a measureagainst multipath phasing, ZP (zero Padding: zero insertion) isperformed by inserting zero into a start portion and an end portion ofdata.

Furthermore, in order to suppress transmission peak power, in atransmitter that performs SC transmission, a precoder normally performsDFT (Discrete Fourier Transform) processing.

CITATION LIST Non Patent Literatures

Non Patent Literature 1: N. Benvenuto, R. Dinis, D. Falconer and S.Tomasin, “Single Carrier Modulation With Nonlinear Frequency DomainEqualization: An Idea Whose Time Has Come-Again”, Proceeding of theIEEE, vol. 98, no. 1, January 2010, pp. 69-96.

Non Patent Literature 2: J. A. C. Bingham, “Multicarrier Modulation forData Transmission: An idea Whose Time Has Come”, IEEE Commun. Mag., vol.28, no. 5, May 1990, pp. 5-14.

SUMMARY Technical Problem

According to the conventional SC block transmission technique describedabove, transmission peak power is suppressed while the effect ofmultipath phasing is reduced. However, with the SC block transmission,the phase and the amplitude become discontinuous between the SC blocks,and thus there is a problem that out-of-band spectrum or out-of-bandleakage occurs. Because the out-of-band spectrum interferes with anadjacent channel, the out-of-band spectrum needs to be suppressed.Further, in a general communication system, a spectral mask is defined,and the out-of-band spectrum needs to be suppressed so as to satisfy themask.

The present invention has been achieved in view of the above problems,and an object of the present invention is to provide a transmissionapparatus, a reception apparatus, and a communication system that cansuppress an out-of-band spectrum.

Solution to Problem

In order to solve the above problems and achieve the object, an aspectof the present invention is a transmission apparatus that transmits ablock signal including a plurality of data symbols, the transmissionapparatus including: a data-symbol generation unit that generates a datasymbol; a symbol arrangement unit that arranges the data symbol and asame-quadrant symbol such that one same-quadrant symbol that becomes asignal point in a same quadrant in a complex plane is inserted per blockat a predetermined position in each block signal to generate a blocksymbol; a CP insertion unit that inserts a Cyclic Prefix into the blocksymbol; and an interpolation unit that performs interpolation processingon the block symbol on which CP insertion has been performed.

Advantageous Effects of Invention

According to the present indention, an effect is obtained where anout-of-band spectrum can be suppressed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a functional configuration example of atransmission apparatus according to a first embodiment.

FIG. 2 is a diagram illustrating an example of the frame configurationused in a communication system that performs SC block transmission.

FIG. 3 is a diagram illustrating an example in which a phase and anamplitude become discontinuous between SC blocks in conventional SCblock transmission.

FIG. 4 is a diagram illustrating an example of fixed symbol arrangementaccording to the first embodiment.

FIG. 5 is a diagram illustrating an example of a block symbol after CPinsertion.

FIG. 6 is a diagram illustrating an example of the frame configurationof the first embodiment.

FIG. 7 is a diagram illustrating an example of a fixed symbol when aQPSK symbol is used as a data symbol.

FIG. 8 is a diagram illustrating a functional configuration example of atransmission apparatus according to a second embodiment.

FIG. 9 is a diagram illustrating an example of processed data in thetransmission apparatus of the second embodiment.

FIG. 10 is an explanatory diagram of an out-of-band leakage suppressioneffect by the transmission apparatus according to the second embodiment.FIG. 11 is a diagram illustrating a functional configuration example ofa transmission apparatus according to a third embodiment.

FIG. 12 is a diagram illustrating an example of arrangement of pilotsymbols in a frequency domain. FIG. 13 is a diagram illustrating anexample of a relation between a time-domain pilot signal and afrequency-domain pilot signal.

FIG. 14 is a diagram illustrating an example of symbol arrangement ofthe present embodiment after correction by a symbol correction unit.

FIG. 15 is a diagram illustrating an example of the frame configurationof the third embodiment when a pilot symbol is inserted into all blocksin a frame.

FIG. 16 is a diagram illustrating an example of the frame configurationincluding both a block in which a pilot symbol is inserted and a blockin which a pilot symbol is not inserted.

FIG. 17 is a diagram illustrating a functional configuration example ofa transmission apparatus according to a fourth embodiment.

FIG. 18 is a diagram illustrating a functional configuration example ofa reception apparatus according to a fifth embodiment.

FIG. 19 is a diagram illustrating a functional configuration example ofa transmission apparatus according to a sixth embodiment.

FIG. 20 is a diagram illustrating an example of symbol arrangement ofthe sixth embodiment.

FIG. 21 is a diagram illustrating 64 QAM constellation and a mappingarea of same-quadrant symbols.

FIG. 22 is a diagram illustrating an example of a block symbol when 64QAM is used.

FIG. 23 is a diagram illustrating an example of a block symbol when 64QAM is used.

FIG. 24 is a diagram illustrating an arrangement example of fixedsymbols according to a seventh embodiment.

DESCRIPTION OF EMBODIMENTS

Exemplary embodiments of a transmission apparatus, a receptionapparatus, and a communication system according to the present inventionwill be explained below in detail with reference to the accompanyingdrawings. The present invention is not limited to the embodiments.

First Embodiment

FIG. 1 is a diagram illustrating a functional configuration example of atransmission apparatus according to a first embodiment of the presentinvention. As illustrated in FIG. 1, the transmission apparatusaccording to the present invention includes a data-symbol generationunit 1, a fixed-symbol arrangement unit (symbol arrangement unit) 2, aCP insertion unit 3, an interpolation unit 4, and a transmissionprocessing unit 5.

The data-symbol generation unit 1 generates a data symbol (for example,a PSK (Phase Shift Keying) symbol and a QAM (Quadrature AmplitudeModulation) symbol). The fixed-symbol arrangement unit 2 arranges onepreassigned fixed symbol (fixed signal) at a predetermined position withrespect to a data symbol to generate a block symbol. The CP insertionunit 3 inserts a CP into the block symbol generated by the fixed-symbolarrangement unit 2. The interpolation unit 4 performs interpolationprocessing on the block symbol after the CP has been inserted. Thetransmission processing unit 5 performs transmission filteringprocessing, analog-signal conversion processing, and the like on theblock symbol after the interpolation processing, and transmits the blocksymbol as an SC block signal (block signal).

Conventional SC block transmission is described here. In the SC blocktransmission, the phase and the amplitude become discontinuous betweenSC blocks. FIG. 2 is a diagram illustrating an example of the frameconfiguration used in a communication system that performs SC blocktransmission. In FIG. 2, d_(k) ^((n)) denotes the k-th symbol of then-th block. FIG. 2 illustrates an example in which the SC block consistsof N_(b) symbols and one frame consists of N_(F)SC blocks. FIG. 3 is adiagram illustrating an example in which the phase and the amplitudebecome discontinuous between SC blocks in the conventional SC blocktransmission. In the example in FIG. 3, the out-of-band spectrum or theout-of-band leakage occurs between the k-th block and the (k+1)th block.Such an out-of-band spectrum interferes with an adjacent channel. In thepresent embodiment, the out-of-band spectrum is reduced by inserting afixed symbol between data symbols and performing CP insertion afterinserting the fixed symbol.

An operation according to the present embodiment is described next. Itis assumed that the number of symbols (the total number of data symbolsand fixed symbols) before CP Insertion into one single-carrier block (SCblock) is N.

The fixed-symbol arrangement unit 2 arranges one preassigned fixedsymbol “A” at a predetermined position with respect to a data symbol.The fixed symbol can be any symbol as long as rules and regulations ofthe communication system to be applied are satisfied, and a symbol, suchas a PSK symbol and a QAM symbol, can be used.

FIG. 4 is a diagram illustrating an example of fixed symbol arrangementaccording to the present embodiment. In the example of FIG. 4, the fixedsymbol “A” is inserted at the (N−N_(CP)+1) th position in the blocksymbol (a symbol group constituting one block). In FIG. 4, d_(k) denotesthe k-th data symbol of data symbols in one block.

FIG. 5 is a diagram illustrating an example of the block symbol after CPinsertion. As illustrated in FIG. 5, the CP insertion unit 3 copies(duplicates) the last N_(CP) symbols in the block symbol after the fixedsymbol has been inserted and adds the symbols to the head of the blocksymbol, as CP insertion processing. FIG. 6 is a diagram illustrating anexample of the frame configuration of the present embodiment. Asillustrated in FIG. 6, the fixed symbol is inserted at the same position(the (N−N_(CP)+1)th position) in each block in the frame. In thismanner, if the ((N−N_(CP)+1)th) symbol at the head of the region to becopied by the CP insertion unit is designated as a fixed symbol, thesymbol at the head of the block becomes a fixed symbol after CPinsertion. In the case of N_(CP)=0, d₀ (the first symbol in the block)in FIG. 5 is set as a fixed symbol.

FIG. 7 is a diagram illustrating an example of the fixed symbol when aQPSK symbol is used as a data symbol. A data symbol is assigned to anypoint of the four points illustrated as a QPSK constellation in FIG. 7according to the information to be transsr.ittea. As illustrated in FIG.7, the first symbol and the (N−N_(CP)+1)th symbol become the fixedsymbols and are fixed to 1+j. FIG. 7 is only an example, and the fixedsymbol is not limited to the QPSK symbol and the fixed symbol value isnot limited to 1+j. In the case of N_(CP)=0, the CP insertion unit 3does not perform copying.

The interpolation unit 4 performs oversampling (processing to increasethe sampling rate, that is, to reduce the sampling interval) by using asignal interpolation formula described, for example, in “B. Porat, “ACourse in Digital Signal Processing”, John Wiley and Sons Inc., 1997”(hereinafter, “Porat Literature”), Oversampling is performed such thatsampling points per symbol becomes L with respect to the time domainsignal input to the interpolation unit 4. That is, oversampling isperformed such that the sampling rate becomes L times with respect tothe input. The oversampling rate is a value indicating how many timesthe sampling rate after oversampling is larger than the input samplingrate.

Specifically, for example, the interpolation unit 4 converts the inputtime domain signal to a frequency domain signal, performs zero insertionprocessing for inserting zero with respect to the frequency domainsignal, and converts the frequency domain signal to the time domainsignal again. In this manner, oversampling can be performed by using thezero insertion processing. Oversampling (interpolation processing) inthe interpolation unit 4 can be performed by using other interpolationmethods. A method of performing interpolation (oversampling) withoutchanging the input time domain signal to the frequency domain signalonce can be used.

An interpolated sample point is added between symbols by theoversampling (interpolation processing) by the interpolation unit 4. Inthis case, oversampling is performed such that the phase and amplitudeof the last sample of the SC block and the first sample (a fixed symbol)of the next SC block are smoothly connected. For example, interpolationis performed by assuming that a fixed symbol point is present subsequentto the last sample point of the SC block, and an interpolated point isadded after the last sample point of the SC block. If it is assumed thatthe oversampling rate is L, the number of samples in an output signal ofthe interpolation unit 4 becomes (N+N_(CP))×L. In the presentembodiment, the “fixed symbol” indicates a symbol with the phase andamplitude being fixed; however, a symbol in a specific quadrant can beused. The processing described above is performed for each of thesingle-carrier block symbols. The oversampling rate L does not need tobe an integer.

As described above, in the present embodiment, the fixed-symbolarrangement unit 2 arranges a fixed symbol at the head position of aregion to be copied by the CP insertion unit 3 with respect to datasymbols for each block. The CP insertion unit 3 performs CP insertion onthe block symbol after the fixed symbol has been inserted. Theinterpolation unit 4 then performs oversampling on the block symbolafter the CP insertion. Thus, continuity of the phase and amplitudebetween blocks can be maintained; therefore, the out-of-band spectrumcan be suppressed.

Second Embodiment

FIG. 8 is a diagram illustrating a functional configuration example of atransmission apparatus according to a second embodiment of the presentinvention. FIG. 8 illustrates a configuration example of theinterpolation unit 4 of the transmission apparatus according to thesecond embodiment. In the present embodiment, an example in which theinterpolation unit 4 in FIG. 1 includes a DFT unit (Fourier transformunit) 41, a waveform shaping filter 42, and an oversampling/IDFT(Inverse DFT) unit (inverse Fourier transform unit) 43 is described. Thedata-symbol generation unit 1, the fixed-symbol arrangement unit 2, theCP insertion unit 3, and the transmission processing unit 5 are similarto those in the first embodiment. Constituent elements having functionsidentical to those of the first embodiment are denoted by like referencesigns in the first embodiment, and redundant explanations thereof willbe omitted.

The DFT unit 41 performs (N+N_(CP))−point DFT processing to convert theinput time domain signal to a frequency domain signal. The waveformshaping filter 42 performs filtering processing to remove a signal otherthan signals in a desired frequency domain on the frequency domainsignal. In the filtering processing, processing such as Nyquistfiltering described in, for example, “T. S. Rappaport, “WirelessCommunications”, 2^(nd) edition, Prentice Hall PTR, 2002” (hereinafter,“Rappaport Literature”) can be used. The filtering processing is notlimited thereto.

The oversampling/IDFT unit 43 increases the number of samples to L timesby zero insertion or the like with respect to the frequency domainsignal having been subjected to the filtering processing (increases thenumber of samples to the number corresponding to the oversampling rateL). Thereafter, the oversampling/IDFT unit 43 generates a time domainsignal by performing the IDFT processing on the frequency domain signal.When the waveform shaping filter 42 does not change the number ofsamples of the signal, the number of samples to be subjected to the IDFTprocessing becomes L·(N+N_(CP)). Instead of the oversampling/IDFT unit43, an oversampling unit that performs oversampling and an IDFT unitthat performs IDFT processing can be provided. Because the DFTprocessing and the IDFT processing are performed, for example, by usingIFFT (Inverse Fast Fourier Transform) and FFT that require a lowcomputation amount, it is desired that (N+N_(CP)) is 2^(P) (P is aninteger equal to or larger than 1) and L is an integer. When thewaveform shaping filter 42 changes the number of samples of the signal,it is desired that the number of samples being an input of the IDFTprocessing is 2^(P′) (P′ is an integer equal to or larger than 1).

If it is assumed that N_(A) is the total number of carriers, in thepresent embodiment, N_(A)=N+N_(CP). However, the total number ofcarriers can be N_(A)>N+N_(CP). In this case, if it is assumed that thewaveform shaping filter does not change the number of points,s_(i)(0≤i≤N+N_(CP)−1) is an output of the waveform shaping filter,0_(1,m) is a vector established by 1×M zeroes, and N_(A)−N−N_(CP) is aneven number, the oversampling/IDFT unit 43 maps s_(i) in the N_(A)carriers, as represented by the following equation (1). Further, zeroinsertion is performed on y to perform oversampling. In this case, thenumber of output samples of the oversampling/IDFT unit 43 can beN_(A)*L. Mapping to the total carriers can be performed by anyprocessing method.

y=[0_(1,(N) _(A) _(-N-N) _(CP) _()/2),S₀,S₁, . . . S_(N+N) _(CP)_(-1,)0_(1,(N) _(A) _(-N-N) _(CN) _()/2)]  (1)

FIG. 9 is a diagram illustrating an example of processed data in thetransmission apparatus of the present embodiment. FIG. 9 illustrates anexample in which BPSK (Binary Phase Shift Keying) is used, assuming thatL=2, N=6, N_(CP)=2, and A=1 is arranged in the fifth symbol as a fixedsymbol. In the example in FIG. 9, zero insertion is used as theoversampling processing. In FIG. 9, to simplify signage, rounding isperformed to four decimal places. As illustrated in FIG. 9, it isunderstood that by arranging the fixed symbol in the fifth symbol, thefixed symbol is inserted into the first and the thirteenth symbols afterthe processing by the oversampling/IDFT unit 43, and a symbol to be aninterpolated point is added after the last symbol of the symbol groupoutput from the CP insertion unit 3. The zero insertion method in thepresent embodiment is only an example, and other zero insertion methodscan be used, for example, zero insertion is performed after cyclic shiftis applied to the signal in the frequency domain.

FIG. 10 is an explanatory diagram of an out-of-band leakage suppressioneffect by the transmission apparatus according to the presentembodiment. FIG. 10 illustrates a transmission signal 101 whenout-of-band leakage suppression using the fixed symbol of the presentembodiment is performed and a transmission signal 102 when out-of-bandleakage suppression is not performed. In FIG. 10, the desired bandfrequency is illustrated in the central portion and the region thatcauses the out-of-band leakage is illustrated on both end sides of thedesired band frequency. As illustrated in FIG. 10, it is understoodthat, in the transmission signal 101 that has been subjected to theout-of-band leakage suppression, the out-of-band leakage decreases byabout 16 dB compared to the transmission signal 102 when the out-of-bandleakage suppression is not performed. In the present example, it isassumed that N_(A)=512, N_(CP)32 16, N=434, and the oversampling rate isL=4, a frequency-domain zero roll-off filter described in the RappaportLiterature is used as the waveform shaping filter, and mapping to thecarriers in the frequency domain is performed as represented by thefollowing equation (2). The signal y becomes an input value to theoversampling/IDFT unit 43.

y=[0_(1,(N) _(A) _(-N-) _(CP) _()/2),S₀,S₁, . . . , S_(N+N) _(CP)_(-1,)0_(1,(N) _(A) _(-N-N) _(CN) _()/2)]  (2)

As described above, according to the present embodiment, after the DFTunit 41 converts the block symbol after CP insertion to a frequencydomain signal, the oversampling/IDFT unit 43 performs oversampling andconverts the oversampled signal to a time domain signal by the IDFT.Therefore, as described in the first embodiment, the continuity of thephase and amplitude between the blocks can be maintained; therefore, theout-of-band spectrum can be suppressed. In the case of N_(CP)=0, the CPinsertion unit 3 in FIG. 8 does not perform copying and the fixed-symbolarrangetflent unit 2 sets d₀ (the first symbol in a block) as a fixedsymbol.

Third Embodiment

FIG. 11 is a diagram illustrating a functional configuration example ofa transmission apparatus according to a third embodiment of the presentinvention. FIG. 11 illustrates a configuration example of theinterpolation unit 4 of the transmission apparatus according to thethird embodiment. The transmission apparatus according to the presentembodiment includes the data-symbol generation unit 1, the fixed-symbolarrangement unit 2, the CP insertion unit 3, a symbol correction unit40, the DFT unit 41, waveform shaping filters 42-1 and 42-2, apilot-signal generation/CP processing unit 6, a frequency-domainmultiplexing unit 7, the oversampling/IDFT unit 43, and the transmissionprocessing unit 5. The data-symbol generation unit 1, the fixed-symbolarrangement unit 2, the CP insertion unit 3, the DFT unit 41, theoversampling/IDFT unit 43, and the transmission processing unit 5 aresimilar to those in the second embodiment. Constituent elements havingfunctions identical to those of the second embodiment are denoted bylike reference signs in the second embodiment, and redundantexplanations thereof will be omitted.

A pilot signal that is a known signal is used in some cases to performsynchronous processing and estimation of a transmission line on thereception side. In the block transmission, the pilot signal (the pilotsymbol) is generally arranged in the frequency domain. In the presentembodiment, an example in which the pilot signal is arranged in thefrequency domain is described.

The pilot-signal generation/CP processing unit 6 generates a time-domainpilot signal and a frequency-domain pilot signal, inputs thefrequency-domain pilot signal to the waveform shaping filter 42-2, andinputs the time-domain pilot signal to the symbol correction unit 40.The pilot-signal generation/CP processing unit 6 can apply CP processing(CP insertion processing) to the time-domain pilot signal. Further, thepilot-signal generation/CP processing unit 6 can perform normalizationon the pilot signals. For example, if it is assumed that the time domainsignals of the pilot signals are q₀, q₁, . . . , q_(N-1), and N_(CP) isthe CP length, the pilot signals become q_(N-NCP), . . . , q_(N-1),q₁,q₀, q₁, . . . , q_(n-1) (N_(CP) is written as NCP in the index) afterthe CP processing. When the CP processing is to be added, thepilot-signal generation/CP processing unit 6 generates, as thefrequency-domain pilot signal, a signal by performing the DFT processingon the signal obtained by inserting the CP into the time domain signalof the pilot signal.

The frequency-domain pilot signal is used for multiplexing and thetime-domain pilot signal is used for calculation of a fixed symbol. Thefrequency-domain multiplexing unit 7 multiplexes a data symbol that isinput via the waveform shaping filter 42-1 and is converted to afrequency domain signal by the DFT unit 41 and a frequency-domain pilotsignal (pilot symbol) input via the waveform shaping filter 42-2 in thefrequency domain. The waveform shaping filters 42-1 and 42-2 are similarto the waveform shaping filter 42 according to the second embodiment.The waveform shaping filter 42-1 performs waveform shaping in thefrequency domain on the output from the DFT unit 41, and the waveformshaping filter 42-2 performs waveform shaping on the pilot symbol in thefrequency domain. The pilot signal is not particularly limited, and anysignal can be used. The time-domain pilot signal is generated on thebasis of the arrangement position of the pilot signal in the frequencydomain.

FIG. 12 is a diagram illustrating an example of arrangement of pilotsymbols in the frequency domain. FIG. 12 illustrates an example in whichthe total number of symbols (after CP insertion) in one block is N′(=N+2N_(CP)), the number of pilot symbols N_(P) in one block is N′/2,and the number of data symbols including fixed symbols in one block isN′/2. In the example of FIG. 12, there are alternate arrangements of thepilot symbols p₀, p₁, . . . , P_(N′/2-1) in the frequency domain and thedata symbols including fixed symbols s₀, s₁, . . . , s_(n′/2-1). FIG. 12is only an example, and there is no limitation on the arrangement of thepilot symbols and the number of the pilot symbols in the block symbol.

Because the pilot symbols and the data symbols including the fixedsymbols are multiplexed in the frequency domain by the frequency-domainmultiplexing unit 7, in order to set the fixed symbol as “A” in the timedomain signal that is the IDFT output (the output from theoversampling/IDFT unit 43), the time-domain pilot signals need to betaken into consideration. When it is assumed that the time domainsignals of the pilot signals are q₀, q₁, q₂, . . . , q_(N/2-1), k′ is afixed symbol insertion position in the time domain, and b_(k′) andc_(k′) are phase rotation and amplitude adjustment performed such thatthe symbol at the predetermined position in the IDFT output becomes “A”,the symbol correction unit 40 obtains a fixed symbol A_(k′), which is acorrected value of the fixed symbol “A” generated by the fixed-symbolarrangement unit 2, as A_(k′)=c_(k′)A-b_(k′)q_(k′). The values of b_(k′)and c_(k′) are determined by the insertion positions of the pilotsignals and the arrangement positions of the fixed symbols in thefrequency domain.

A specific example is described below. To simplify the description, asignal that has not been subjected to oversampling is used here. It isassumed that the number of data symbols after CP insertion is N_(D)=N′/2and the number of pilot symbols is N_(T)=N′/2. In the present example,it is assumed that the CP-inserted data symbols are x₀, x₁, . . . ,x_(ND-1) and the pilot symbol p_(z) arranged in the frequency domain isrepresented by the following equation (3). The pilot symbol q in thetime domain after the IDFT processing becomes as represented by thefollowing equation (4).

p _(z)=[0, p ₆, 0,p ₁,0, . . . , 0,p _(N) _(P-1) ]^(T)  (3)

q=[q ₁ ^(T), -q₁ ^(T)]^(T)  (4)

If it is assumed that the DFT-processed data signals (x₀, x₁, . . . ,x_(ND-1)), which are arranged in the frequency domain, are representedby the following equation (5), and a constant b is a normalizationconstant, the data signal t in the time domain after the IDFT processingbecomes as represented by the following equation (6).

s _(z)=[s ₀, 0,s ₁, 0,s ₂, 0, . . . , 0, s _(N) _(b-1) , 0]^(T)  (5)

t=b[t ₁ ^(T) , t ₁ ^(T)]^(T)  (6)

The pilot signal and the DFT-processed data signal multiplexed in thefrequency domain become as represented by the following equation (7),and the time domain signal after the IDFT processing becomes asrepresented by the following equation (8).

r=p _(z) +s _(z)  (7)

y=t+q  (8)

In the time domain, when it is assumed that t_(1,0) is the first elementof t₁, t_(1,0)=x₀. Therefore, when it is desired to set the fixed signal“A” as y₀=A in a symbol time n=0, it siiffices that a symbol asrepresented by the following equation (9) is inserted into the datasymbol. In the present example, to simplify the description, descriptionof the normalization constant and phase rotation is omitted. Phaserotation and amplitude adjustment need to be performed in the equation(9), according to the symbol arrangement in the frequency domain.

$\begin{matrix}{x_{0} = {A_{0}^{\prime} = {\frac{1}{b}( {A - q_{1,0}} )}}} & (9)\end{matrix}$

FIG. 13 is a diagram illustrating an example of a relation between thetime-domain pilot signals and the frequency-domain pilot signals. InFIG. 13, the arrangement of the data symbols and the pilot symbols inthe frequency illustrated in FIG. 12 is presupposed. As illustrated inFIG. 13, in the frequency arrangement illustrated in FIG. 12, the IDFTprocessing is performed by designating a signal in which the portions ofthe data symbols (including the fixed symbols) are replaced by 0 as aninput of the IDFT processing, to obtain the time-domain pilot signals.In FIG. 13, to simplify the description, time-domain pilot signals thatare not subjected to oversampling are illustrated. However, it ispossible to use pilot signals having been subjected to oversampling, forexample, zero insertion, in the frequency domain.

In the present embodiment, because the pilot symbols are inserted in thefrequency domain, the value of the fixed symbol changes according to theinsertion position of the pilot signals and the fixed symbol. Therefore,the processing described above is performed for each block. However, ifthe insertion positions of the pilot signals and the fixed symbol arefixed between the blocks, it is possible to obtain A_(k)′ once andthereafter use A_(k)′ that is already obtained. FIG. 14 is a diagramillustrating an example of symbol arrangement of the present embodimentafter correction by the symbol correction unit 40. In FIG. 14, it isassumed that the total number of symbols before the CP insertion in oneblock is N and the number of pilot symbols N_(P) in one block is N′/2.To maintain the continuity of the phase and amplitude between blocks,phase rotation and amplitude adjustment can be applied to the fixedsymbol or a fixed signal can be added. Further, in FIG. 14, it isdescribed that the (−N_(CP)+1)th symbol and (N/2−N_(CP)+1)th symbol areadjusted; however, only the (−N_(CP)+1)th symbol can be adjusted.

FIG. 15 is a diagram illustrating an example of the frame configurationof the present embodiment (the fixed symbols and the data symbols afterthe correction by the symbol correction unit 40) when pilot symbols areinserted into all the blocks in a frame. As illustrated in FIG. 15, thecorrected fixed symbols are inserted such that the insertion positionsof the fixed symbols become the same in the respective blocks.

The first embodiment is an embodiment in which a block symbol consistsof only data symbols, and the second embodiment is an embodiment inwhich a block symbol consists of pilot symbols and data symbols. If afixed symbol is set in the time domain such that the fixed symbol isarranged at the same position in each block, the frame configurationcombining the two embodiments can be used. Also in this case, an effectof suppressing the out-of-band spectrum can be acquired. FIG. 16 is adiagram illustrating an example of the frame configuration includingboth a block in which a pilot symbol is inserted and a block in which apilot symbol is not inserted. In FIG. 16, in the i-th block, a pilotsymbol is not inserted; therefore, the processing similar to that of thefirst embodiment is performed, and in the (i−1)th block, a pilot symbolis inserted; therefore, the processing similar to that of the secondembodiment is performed.

As described above, according to the present embodiment, when the pilotsymbol is multiplexed in the frequency domain and transmitted, thesymbol correction unit 40 corrects the fixed symbol such that theIDFT-processed fixed symbol after being multiplexed with the pilotsignal has a predetermined value at a predetermined position, on thebasis of the arrangement position of the pilot signal. Accordingly, evenif the pilot signal is multiplexed, the continuity of the phase andamplitude between blocks can be maintained; therefore, the out-of-bandspectrum can be suppressed. Also in the present embodiment, in the caseof N_(CP)=0, the first data symbol in a block can be set as a fixedsymbol, and symbol correction can be performed by using a pilot symbolin the time domain.

Fourth Embodiment

FIG. 17 is a diagram illustrating a functional configuration example ofa transmission apparatus according to a fourth embodiment of the presentinvention. The transmission apparatus according to the presentembodiment includes the data-symbol generation unit 1, and thefixed-symbol arrangement unit 2, the CP insertion unit 3, the symbolcorrection unit 40, the interpolation unit 4, a pilot-signalgeneration/CP processing unit 61, a time-domain multiplexing unit 8, andthe transmission processing unit 5. The data-symbol generation unit 1,the fixed-symbol arrangement unit 2, the CP insertion unit 3, theinterpolation unit 4, and the transmission processing unit 5 are similarto those in the first embodiment. The symbol correction unit 40 issimilar to that in the second embodiment. Constituent elements havingfunctions identical to those of the first or second embodiment aredenoted by like reference signs in the first or second embodiment, andredundant explanations thereof will be omitted.

In the third embodiment, an example in which the pilot signals aremultiplexed in the frequency domain has been described. In the presentembodiment, the pilot signals are multiplexed in the time domain. Thepilot-signal generation/CP processing unit 61 generates time-domainpilot signals and inputs the pilot signals to the time-domainmultiplexing unit 8 and the symbol correction unit 40. The interpolationunit 4 generates time-domain data symbols (including a fixed symbol) asin the first embodiment, and the time-domain multiplexing unit 8multiplexes the time-domain data symbols (including a fixed symbol) andthe time-domain pilot signals in the time domain. The time-domainmultiplexing can be performed as y_(k)=s_(k)+p_(k), for example,assuming that s_(k) is a data signal in the time domain, p_(k) is apilot signal in the time domain, and the multiplexed signal is y_(k).

As described above, according to the present embodiment, when the pilotsymbols are multiplexed in the time domain and transmitted, the symbolcorrection unit 40 corrects the fixed symbol. Accordingly, even if thepilot signals are multiplexed in the time domain, the continuity of thephase and amplitude between blocks can be maintained; therefore, theout-of-band spectrum can be suppressed.

Fifth Embodiment

FIG. 18 is a diagram illustrating a functional configuration example ofa reception apparatus according to a fifth embodiment of the presentinvention. The reception apparatus according to the present embodimentreceives an SC block signal transmitted by the transmission apparatusdescribed in the first to fourth embodiments.

The reception apparatus according to the present embodiment is such thata reception/synchronization unit 10 performs synchronous processing suchas frame synchronization, frequency synchronization, and symbolsynchronization on a received signal (an SC block signal). A CP removalunit 11 performs CP removal on the received signal after the synchronousprocessing. A DFT unit 12 performs DFT processing on the CP-removedreceived signal. A transmission-line estimation unit 13 performsestimation of a transmission line in accordance with the DFT-processedsignal. A sampling/interference removal unit 14 performs downsampling onthe DFT-processed signal. An FDE unit (equalization unit) 15 performsFDE (Frequency Domain Equalizer: frequency domain equalization)processing on the basis of the downsampled signal and the estimationresult of the transmission line. An IDFT unit 16 performs IDFTprocessing on the FDE-processed signal. A fixed-symbolremoval/demodulation/decoding unit 17 removes a fixed symbol from theIDFT-processed signal and performs demodulation and decoding processingon the signal after the fixed symbol has been removed. In theconfiguration example of FIG. 18, the fixed-symbolremoval/demodulation/decoding unit 17 performs removal, demodulation,and decoding of the fixed symbol. However, a fixed-symbol removal unitthat removes a fixed symbol and a demodulation/decoding unit thatperforms demodulation and decoding can be separately provided.

As described in the first to third embodiments, on the transmissionside, oversampling is performed on the DFT-processed signal includingthe CP, and thus the CP component is in a data area. Therefore, CPinterference removal is performed on the reception side as required. Forexample, the synchronization unit 10 can estimate the value of the CPsymbol and the interference value. Therefore, the synchronization unit10 can provide the CP estimation value to the sampling/interferenceremoval unit 14 to remove CP interference. Further, thetransmission-line estimation unit 13 can perform CP estimation.

As described above, in the present embodiment, the reception apparatusthat receives the SC block signal transmitted by the transmissionapparatus described in the first to third embodiments has beendescribed. The reception apparatus performs demodulation and decoding onthe received signal after downsampling and removal of the fixed symbolhave been performed. Accordingly, it is possible to perform demodulationand decoding processing on the signal that is transmitted after thefixed symbol is inserted thereinto and interpolation processing isperformed thereon.

Sixth Embodiment

FIG. 19 is a diagram illustrating a functional configuration example ofa transmission apparatus according to a sixth embodiment of the presentinvention. The transmission apparatus according to the presentembodiment includes the data-symbol generation unit 1, a same-quadrantmapping unit 21, the CP insertion unit 3, the DFT unit 41, the waveformshaping filter 42, the oversampling/IDFT unit 43, and the transmissionprocessing unit 5. The data-symbol generation unit 1, the CP insertionunit 3, the DFT unit 41, the waveform shaping filter 42, theoversampling/IDFT unit 43, and the transmission processing unit 5 aresimilar to those as in the second embodiment. Constituent elementshaving functions identical to those of the second embodiment are denotedby like reference signs in the second embodiment, and redundantexplanations thereof will be omitted.

In the first to fourth embodiments, an example in which a fixed symbolis arranged at a predetermined position has been described. In thepresent embodiment, a symbol that becomes a signal point in the samequadrant (hereinafter, “same-quadrant symbol”) is arranged at apredetermined position in a complex plane (an IQ plane) instead of thefixed symbol.

The same-quadrant mapping unit 21 performs mapping such that a symbol ata predetermined position in a block becomes the same-quadrant symbol inthe time domain. FIG. 20 is a diagram illustrating an example of symbolarrangement of the present embodiment. A symbol A^((i)) denotes asame-quadrant symbol in the i-th block. For example, A^((i-1)) andA^((i)) are not always the same symbol, but are mapped in the samequadrant. In this manner, by using the same-quadrant symbols instead ofthe fixed symbols that have the same value, the same-quadrant symbol caninclude data bits, thereby enabling data loss to be minimized.

FIG. 21 is a diagram illustrating 64 QAM constellation and a mappingarea of the same-quadrant symbols. When 64 QAM symbols are used as thedata symbols, the same-quadrant symbol is mapped at a point, forexample, in the upper right quadrant (an area surrounded by a dottedline in FIG. 21). In the case of FIG. 21, it suffices that the symbolA^((i)), which is the same-quadrant symbol in the i-th block, isarranged in the area indicated by the dotted line. Therefore, high-ordertwo bits of the same-quadrant symbol are fixed to “00” and the remaininglow-order four bits can be used as data bits. The high-order two bits ofthe same-quadrant symbol arranged at a predetermined position in thetime domain are fixed to “00” for all the blocks, and the low-order fourbits take arbitrary values. In the example of FIG. 21, the mapping areaof the same-quadrant symbol is assumed to be in one quadrant; however,the same-quadrant symbol can be mapped in a narrower area in the samequadrant.

Even if the pilot symbol is inserted, as in the second embodiment, if itis assumed that A_(k) ^((i)′) is the same-quadrant symbol and k′ is aninsertion position, it suffices that the same-quadrant symbol iscorrected such that, the IDFT output becomes A^((i)), assuming thatA_(k′) ^((i)′)=c_(k′)A^((i))−b_(k′)q_(k′), while taking the pilotcomponent into consideration.

FIGS. 22 and 23 are diagrams illustrating examples of a block symbolwhen 64 QAM is used. FIG. 22 illustrates an example in which the(N−N_(CP)+1)th symbol is set as the same-quadrant symbol, high-order twobits of the same-quadrant symbol are fixed to “01”, and the sameprocessing is applied to all the blocks. FIG. 23 illustrates an examplein which the (N−N_(CP)+1)th symbol is set as the same-quadrant symbol,high-order four bits of the same-quadrant symbol are fixed to “0100”,and the same processing is applied to all the blocks. In the example ofFIG. 22. the number of data bits per block symbol becomes 6N−2 bits, andin the example of FIG. 23, the number of data bits per block symbolbecomes 6N−4 bits.

In the present embodiment, a configuration example in whichinterpolation using DFT is performed has been described. However, asdescribed in the first embodiment, the same-quadrant symbol can be usedinstead of the fixed symbol also in the configuration example in whichthe interpolation unit 4 is used. Further, the reception apparatus thatreceives the signal transmitted from the transmission apparatusaccording to the present embodiment performs removal of the fixed bitsof the same-quadrant symbol instead of removal of the fixed symbol, andhandles the remaining bits after removal of the fixed bits as data bitsto perform the decoding processing, in the fixed-symbolremoval/demodulation/decoding unit 17 of the reception apparatusdescribed in the fifth embodiment.

As described above, according to the present embodiment, thesame-quadrant symbol is arranged instead of the fixed symbol. Therefore,data loss can be reduced as compared to the case of using the fixedsymbol.

Furthermore, in the present embodiment, an example of performing blocktransmission has been described. However, the present invention is notlimited thereto, and can be applied to a transmission apparatus and areception apparatus of various systems including a wired system.Further, generation of the fixed symbol and the same-quadrant symbol hasbeen described. However, generation of these symbols is not limited tothe examples described above, and for example, a plurality of methodscan be combined. The configurations of the transmission apparatus andthe reception apparatus are not limited to the apparatus configurationsdescribed in the respective embodiments. As the interpolation method andthe transmission processing method used for oversampling and the likedescribed in the present embodiment, any method can be used as long asthe continuity between the first and the last samples can be maintainedin the SC block symbol.

Seventh Embodiment

The transmission apparatus according to a seventh embodiment isdescribed next. FIG. 5 of the first embodiment illustrates an example ofN_(CP)>0. In the present embodiment, as an expansion of N_(CP)=0, amethod of arranging fixed symbols for suppressing the out-of-bandspectrum is described.

FIG. 24 is a diagram illustrating an arrangement example of fixedsymbols according to the present embodiment. In the example of FIG. 24,in the case of N_(CP)=0, to improve the effect of suppressing theout-of-band spectrum, a fixed symbol is inserted around the first symboland around the last symbol in a block. In FIG. 24, a blank portion whereno character is written indicates a data symbol and F_(i) denotes afixed symbol. In the present embodiment, it is assumed thatN_(L)+N_(R)+1 symbols of the N symbols in one block are fixed symbols.N_(R) denotes the number of fixed symbols continuous to the right sidefrom the first symbol and denotes the number of fixed symbols continuousto the left side from the last symbol. In the present embodiment, theN_(L)+N_(R)+1 symbols are referred to as a “fixed symbol series”. Asillustrated in FIG. 24, the fixed symbol series is expressed as[F_(−NL), F_(−NL+1), F_(−NL+2), . . . , F⁻¹, F₀, F₁, . . . , F_(NR)].The subscripts NL and NR respectively denote N_(L) and N_(R). There isno limitation on the values of the respective symbols F_(i) in the fixedsymbol series, and two or more of F_(i) can have the same value. Ifpower normalization is to be performed after arrangement of the fixedsymbol series in the block symbol, F_(i) can be set to different values,respectively. For example, as F_(i), a symbol such as M-PSK (M-ary-PhaseShift Keying) and M-QAM (M-ary Quadrature Amplitude Modulation) can beused, or several of F_(i) can be set to zero. Further, the seriesdescribed in “D. C. Chu, “Polyphase Codes With Good Periodic CorrelationProperties”, IEEE Transactions on Information Theory, pp. 531-532, July1972” can be used as the fixed symbol series.

To obtain the spectrum suppression effect, the same fixed symbol seriesis used in all the blocks, and the same fixed symbols are arranged atthe same positions between the blocks. The method of arranging the fixedsymbol series is as described below. F₀ of the fixed symbol series isarranged at the first position in the block. With reference to thesepositions, the fixed symbols are arranged on the right and left of thereference position in the order of [F_(−NL), F_(−NL+1), F_(NL+2), . . ., F⁻¹, F₀, F₁, . . . , F_(NR)] such that the relative sequence of thefixed symbol series is not changed. Specifically, the fixed symbolseries is divided into a symbol group (a first symbol group) on the leftside of the reference position (the position of F₀) and a symbol groupincluding the reference position and on the right side of the referenceposition [F₀, F₁, . . . , F_(NR)] (a second symbol group). [F₀, F₁, . .. , F_(NR)] are arranged in order from the first position in the block.Further, because N_(CP)=0, the last symbol of the previous block isarranged before the first symbol of each block. Therefore, by arranging[F_(−NL), F_(−NL+1), F_(−NL+2), . . . , F⁻¹] in the last portion of eachblock, these symbols ([F_(−NL), F_(−NL+1), F_(−NL+2), . . . , F⁻¹]) arearranged on the left side of the reference position (the first symbol).

When the interpolation processing is performed as in the firstembodiment, an interpolated sample point is added between symbols.However, due to circularity of the IDFT output, the interpolated pointadded behind the last symbol becomes a point that interpolates betweenthe last symbol F⁻¹ and the first symbol F₀. Accordingly, the continuityof the phase and amplitude between blocks can toe maintained; therefore,the out-of-band spectrum can be suppressed. Further, by increasing N_(L)and N_(R), an effect of further suppressing the out-of-band spectrum canbe acquired.

In the present embodiment, the fixed symbol series becomes the samebetween the blocks. However, the present embodiment can be configuredsuch that the fixed symbol series becomes the same-quadrant symbolbetween the blocks as described in the sixth embodiment. As a specificexample, for example, in the case where the 64 QAM signal as illustratedin FIG. 21 is used, if the first (high-order) bits of a symbol havingthe symbol number N are fixed to “00”, the first two bits of a symbolhaving the symbol number 1 are fixed to “01”, and the first two bits ofa symbol having the symbol number 2 are fixed to “11”, it is possible touse 4×3=12 bits in total as data bits. As described in the third andfourth embodiments, when the pilot symbols are multiplexed, the fixedsymbol series of the present embodiment can be used.

As described above, according to the present embodiment, with referenceto the position of the first symbol of the block symbol, the same fixedsymbol series is arranged in each block before and after the referenceposition. Accordingly, the continuity of the phase and amplitude betweenblocks can be maintained; therefore, the out-of-band spectrum can besuppressed.

INDUSTRIAL APPLICABILITY

As explained above, the transmission apparatus, the reception apparatus,and the communication system according to the present invention areuseful in a communication system that performs SC block transmission.

REFERENCE SIGNS LIST

1 data-symbol generation unit, 2 fixed-symbol arrangement unit, 3 CPinsertion unit, 4 interpolation unit, 5 transmission processing unit, 6,61 pilot-signal generation/CP processing unit, 7 frequency-domainmultiplexing unit, 8 time-domain multiplexing unit, 21 same-quadrantmapping unit, 40 symbol correction unit, 41 DFT unit, 42, 42-1, 42-2waveform shaping filter, 43 oversampling/IDFT unit, 10reception/synchronization unit, 11 CP removal unit, 12 DFT unit, 13transmission-line estimation unit, 14 sampling/interference removalunit, 15 FDE unit, 16 IDFT unit, 17 fixed-symbolremoval/demodulation/decoding unit.

1. A transmission apparatus that transmits a block signal including aplurality of data symbols, the transmission apparatus comprising: adata-symbol generation circuit that generates a data symbol; a symbolarrangement circuit that arranges the data symbol and a fixed symbol ina time domain to generate a block symbol, the fixed symbol indicating asymbol with the phase and amplitude being fixed in a complex plane; andan interpolation circuit that performs interpolation processing on theblock symbol, wherein the symbol arrangement circuit arranges the fixedsymbol on a head of the block symbol.
 2. The transmission apparatusaccording to claim 1, wherein the symbol arrangement circuit arranges afixed symbol series at a position of a plurality of continuous-arrangedsymbols including a head of symbols in the block symbol, the fixedsymbol series being constituted by a plurality of the fixed symbols.